The invention relates to a holder for workpieces during treatment.
In many processes, workpieces are treated, for example, by coating, spraying, etching, ion implantation, etc., in a manner which undesirably heats the workpiece. Maintaining the workpiece relatively cool, i.e., below temperatures where damage can occur to the workpieces or masking materials is a particular problem in treating semiconductor wafers in vacuum.
Typically, workpieces such as semiconductor wafers are mounted on individual cylindrical holders and transported in a treatment area in which vacuum is maintained so that each workpiece is uniformly treated. During treatment, heat is produced and must be efficiently and effectively transferred away from the workpieces.
One way in which this can be done is to mount the workpiece holder in contact with a plate and to slide the workpiece holders along the plate while a cooling fluid is circulated underneath or through the plate. U.S. Pat. No. 4,187,801 issued Feb. 12, 1980 describes an apparatus of this type. While this approach is effective, it necessitates a relatively complex transporting system in which the workpiece holders must be slid and maintained in contact with the plate. Another approach to maintaining the workpieces cool is to mount them on an elastomeric disc which is in turn mounted on a workpiece holder. Preferably, the disc has a number of holes in it which are communicated to a vacuum source so that the workpiece is drawn to and held tightly on the elastomeric disc. U.S. Application, Ser. No. 953,214, filed Oct. 20, 1978 describes a workpiece holder of this type, and the patent to Jones U.S. Pat. No. 4,139,051 describes a similar holder.
The present invention relates to a unique workpiece holder particularly effective for cooling semiconductor workpieces during treatment in which a casing which is preferably substantially cylindrical and resembles a "hockey puck" includes a hollow interior space filled with a composition which absorbs heat from the workpiece during treatment, thus maintaining the workpiece relatively and satisfactorily cool. The workpieces are mounted on an upper surface of the holder with a bore preferably extending between the upper and lower surfaces for applying a vacuum to that upper surface to hold a workpiece thereon. Alternatively, an overpressure can be applied on top of the wafer to insure contact between the workpiece and holder.
Any of a number of different compositions including Glauber's salt (sodium sulfate decahydrate), and calcium chloride hexahydrate provide satisfactory heat absorbing characteristics. A circular groove is preferably provided in the peripheral surface between the upper and lower surfaces so that the holder can be readily transported on rails which enter into the groove and rotated or oscillated during treatment. The upper surface is preferably thick enough to prevent bowing of that surface when vacuum is applied or with changes in ambient pressure. Other means of pressure relief such as a bellows port can alternatively be used.
In a first embodiment, a plurality of curved, generally radially extending vanes can be provided within the interior space to promote generally radial flow during rotation or oscillation and thus good heat distribution within the interior space. After treatment, the holder must be cooled and this can be accomplished by rotating or oscillating in a refrigerated environment, the radial flow promoted by the vanes cooling all of the areas of the interior space at substantially the same time.
In a second embodiment of the present invention, the "hockey puck" is formed with top and bottom portions which are threaded together with an O-ring to provide a satisfactory seal which is maintained under treatment conditions. Further, the surface on which the elastomeric disc and the semiconductive wafer are retained is preferably provided with a plurality of circumferential grooves, each of which is connected by a downwardly extending bore to a manifold which extends radially to a nipple at the side of the workpiece holder to which a vacuum source can be coupled. Thus, no bore is provided through the space in which the heat conducting material is contained. This makes the structure mechanically simpler and, in addition, the workpiece holder does not have to be moved in order to be attached to a vacuum source. A flexure plate is preferably utilized in a recess in the peripheral surface between the upper and lower surfaces for latching the top to a clamp.
Other objects and purposes of the invention will be clear from the following detailed description of the drawings.